The present invention relates to a projection display device, including liquid crystal panels, DMD elements or other display elements for forming optical images, and a single projecting means for projecting the formed images on an enlarged scale. In particular, the invention relates to a projection display device including a mechanism for shifting the projecting means to vary the range of video light projection on a screen.
A known liquid crystal projector operating as a projection display device includes liquid crystal panels as display elements, which panels can be irradiated with light from a light source so that the images on the panels can be projected on an enlarged scale. In recent years, transmission and reflection display elements have been increasingly reduced in size, and they have exhibited improved performance, such as improved resolution. This has lead to the development of projection displays for various uses, such as displaying video images and computer images. There is a demand that these projection displays be small in size, high in luminance, uniform in screen luminance, and capable of displaying high contrast images.
In general, the projection display device is disposed in front of a screen. In this regard, it is essential that the projection display device should not obstruct the screen when one views the screen. For example, each of Japanese Unexamined Patent Publications No. H10-171044 and No. 2001-215610 discloses an apparatus including display elements and a projection lens, which is part of a projecting optical system. The optical axis of the projection lens is displaced upward or in another direction in parallel by a suitable distance relative to the display elements. The images projected onto a screen by this projection display device are shifted in the direction of lens displacement and in proportion to the distance of lens displacement. This makes the projection display device less obstructive to the screen and consequently more convenient.
A commercialized product includes a projection lens, which is part of a projecting optical system, and a shifting mechanism for shifting the lens. In order to improve the degree of freedom of the positions of the projected images, the shifting mechanism makes it possible to set any distances by which the optical system can be shifted continuously.